1. Field of the Invention
The present invention concerns optical fiber ribbons. It is more particularly concerned with an optical fiber multi-ribbon in which the optical fibers are those of at least two initially independent ribbons disposed side by side in a common plane and assembled together in a common exterior sheath surrounding them.
2. Description of the Prior Art
Accordingly, a multi-ribbon of this kind can advantageously include a large number of optical fibers to be used to fabricate a high-density optical cable, for example a telecommunication cable.
Document EP-A-0 636 913 discloses an optical fiber ribbon in which the fibers are disposed and assembled together side by side. In particular, this ribbon includes at least two independent initial ribbons and a common exterior sheath around the initial ribbons. The various fibers of each initial ribbon, which have an individual protective coating, are disposed side by side and surrounded by a common assembly sheath.
The exterior protective coating of each fiber is of a conventional, relatively hard resin selected from thermosetting resins and resins that can be cross-linked, for example by ultraviolet light. This resin is used as the main constituent of the sheath assembling the fibers of each of the initial ribbons and the common exterior sheath surrounding the various initial ribbons.
In particular, the common exterior sheath around the initial ribbons includes this main constituent of relatively hard resin and a component which is not very compatible with the main constituent. In a preferred embodiment, a reactive functional group is introduced into this component and thereby incorporated into the resin forming the main constituent when the latter is cross-linked. In another preferred embodiment the component of low compatibility which is cross-linked on its own has a lower Young's modulus than the main constituent and forms a discontinuous phase of five microns or less after the resin is cross-linked. The addition of a low compatibility component of this kind into the resin constituent decreases the coefficient of friction of the resultant resin into which it has been incorporated.
These embodiments are relatively complex. Further, the absence of sufficient friction between the common exterior sheath and the sheaths of the initial ribbons means that the geometrical retention of the ribbons is not always satisfactory for mass splicing by fusing the fibers of these initial ribbons or of this multi-ribbon to those of other similar initial ribbons or another similar multi-ribbon. Furthermore, it is not easy to separate the multi-ribbon into its initial ribbons. This separation exploits the fact that the exterior resin including the low compatibility component is in fact peelable.
An aim of the present invention is to solve these problems for easy manufacture of a multi-ribbon that is easily cut to separate the initial ribbons.